This invention relates to improvements in the heat exchanger apparatus in solution heat pump systems and in particular to apparatus and methods for improving the efficiency of heat exchange in the desorber and absorber in a waste heat powered solution heat pump application to up-grade waste heat by temperature boosting.
Many solution heat pump apparatus and methods have been developed. One of the first proposed practical uses of an absorption heat pump was reported by D. A. Williams and J. B. Tredemann at the Intersociety Energy Conversion Engineering Conference, 9th Proceedings, August, 1974 in a paper entitled Heat Pump Powered by Natural Thermal Gradients.
Additional work has been reported in various recent publications including patents and patent applications, including the following:
U.S. Pat. No. 4,333,515, issued June 8, 1982, inventor William H. Wilkinson et al entitled Process and System for Boosting The Temperature of Sensible Waste Heat Sources;
U.S. Pat. No. 4,338,268, issued July 6, 1982, inventor William H. Wilkinson et al, entitled Open Cycle Thermal Boosting System;
U.S. Pat. No. 4,402,795, issued Sept. 6, 1983, inventor Donald C. Erickson, entitled Reverse Absorption Heat Pump Augmented Distillation Process.
U.S. patent application Ser. No. 667,747, filed Nov. 2, 1984, inventors Michael L. Lane and Lowell T. Whitney entitled Solution Heat Pump Apparatus and Method.
The foregoing patents, patent application, and the references cited therein represent the current state of the temperature boosting art using solution heat pump technology and the heat exchanger apparatus used therein and these disclosures are incorporated herein by reference in their entirety.
In general, waste heat from industrial or other sources can be boosted to higher temperature levels by combining at least one relatively high pressure Rankine vapor generation cycle with at least one solution heat pump cycle. In a typical system, waste heat is utilized to boil off a fluid termed a refrigerant in the Rankine cycle evaporator to provide a source of vapor to an absorber in the solution heat pump. In the absorber, the refrigerant vapor is contacted with a binary working solution containing absorbent and refrigerant. As the refrigerant vapor is absorbed into the binary absorbent solution, its latent heat of absorption is given off to a heat exchanger at a temperature higher than the temperature of the waste heat source. The dilute binary solution from the absorber is throttled to reduce the pressure and then introduced into a relatively low pressure desorber in heat exchanging contact with a source of waste heat where a portion of the refrigerant is desorbed as vapor from the binary solution by the addition of waste heat. The desorbed vapor from the solution is then condensed by contact with a colder heat exchanger at a temperature less than the temperature of the vapor, and the condensate or refrigerant is then pumped to the evaporator for reevaporation. The concentrated solution is recycled from the desorber to the absorber, preferably through a heat exchanger where heat is exchanged with the dilute working solution being conveyed from the absorber to the desorber.
Waste heat sources which have been used to power solution or absorption heat pumps, as described, can be obtained from either sensible heat, latent heat or both. Utilization of a sensible waste heat source has been maximized by extracting successive portions of heat for use first in the Rankine cycle evaporator section and then in the heat pump cycle desorber section of a solution or absorption heat pump. Multiple cycle systems can also be employed to boost the temperature of a portion of the waste heat to higher levels than obtainable in single cycle systems.
In absorption systems, not only must efficient heat transfer occur in the absorber and desorber sections but also efficient mass transfer of refrigerant into and out of solution must occur. In prior absorption refrigeration systems, the desorber section of the system typically consisted of a chamber having heat exchange tubes immersed in a pool of binary solution. Heat transfer was limited by the surface area of the tubes, residence time of the solution, and back mixing, which occurred as new solution was fed into the chamber and as convective recirculation occurred in the pool. Mass transfer was similarly limited by what typically was the relatively small surface area of the pool of solution.
In particular, heat exchanger apparatus comprising vertical tubes with the waste heat source inside the vertical tubes and the concentrated LiBr-water working fluid in heat exchanging contact with the outside of the tubes has exhibited inefficiencies in practice as previously described.
Likewise, the prior absorber section heat exchanger with the heat being transferred from the working fluid on the outside of the tubes during absorption to the fluid on the inside of the tubes have also not provided the requisite efficiency heat exchange for economic utilization of such systems. Different heat exchanger designs, as previously shown, have attempted to solve some of these problems by structural arrangements to increase residence time of the working fluid by designs which formed smaller pools of working fluid in contact with the outer surface of the vertical tubes. Such apparatus were, however, large and expensive and has enjoyed only limited success.
It is, therefore, an objective of this invention to provide an improved heat exchanger design and method for exchanging heat between a waste heat source and a binary working fluid preferably in an absorption heat pump unit and in particular the desorber section thereof.
It is also an objective of this invention to provide an improved heat exchanger design, and method for exchanging heat between a binary working fluid and another fluid preferably in an absorption heat pump unit and in particular in the absorber section thereof.
It is a further objective of the present invention to incorporate improved design of the present invention in a vertical tube heat exchanger where the waste heat source is contained in the vertical tubes and the binary working fluid uniformly contacts the outside of the vertical tubes whereby a refrigerant, typically water, is desorbed from the binary fluid and the water vapor is subsequently condensed and the reconcentrated binary fluid is circulated to the absorber section of the solution heat pump.
It is still a further objective of the present invention to incorporate the improved design of the present invention in a vertical tube heat exchanger where the binary working fluid during absorption contacts the outside of the vertical tubes and efficiently transfers the heat of absorption to the fluid inside of the tubes.